Twin, or dual, scroll turbocharger configurations may be used in turbocharged engines. A twin scroll turbocharger configuration may separate an inlet to a turbine into two separate passages connected to exhaust manifold runners. In this way, exhaust from the engine cylinders, whose exhaust gas pulses may interfere with each other, are fluidically separated.
For example, on an 14 engine with a cylinder firing order of exhaust manifold runners 1-3-4-2, exhaust manifold runners 1 and 4 may be connected to a first inlet of a twin scroll turbine and exhaust manifold runners 2 and 3 may be connected to a second inlet of said twin scroll turbine, where the second inlet is different and fluidically separated from the first inlet. In this way, separating exhaust gas pulses may result in an increase in efficiency of exhaust gas delivery to a turbine in some cases.
However, under some engine operating conditions, separating exhaust gas pulses as described above may reduce an efficiency of exhaust gas delivery to a turbine. For example, under certain engine operating conditions, e.g., high speed and high load conditions, separating exhaust gas pulses may result in an increase in backpressure and pumping work. This increase in backpressure and pumping work may be due to more restrictive, lower volume passages between the exhaust and the turbine in a dual scroll turbine, as compared to a passage that is not separated in a single scroll turbine. As such, the amount of exhaust gas in the cylinder may raise the pressure in the lower volume passages compared to the relatively larger volume, unseparated passage. The increased backpressure may also result in higher levels of hot residual gas in the cylinder, and may reduce the engine's output power.
One example approach for reducing backpressure and pumping work in a twin scroll turbocharger has been shown by Styles et al. in US 2014/0219849. Herein, systems positioning a branch communication valve between a first scroll and a second scroll in a twin (e.g., dual) scroll turbocharger system is provided. In an example, a branch communication valve may be positioned adjacent to a dividing wall separating a first scroll and a second scroll of the twin turbocharger. In an open position, the branch communication valve may increase fluid communication between the first scroll and the second scroll, and in a closed position, the branch communication valve may decrease fluid communication between the first scroll and the second scroll. In some examples, each scroll may include a corresponding wastegate and a corresponding wastegate valve to control the amount of exhaust gas which passes through turbine.
The inventors herein have recognized a potential issue with the example approach of Styles et al. For example, there may be cost, weight, and packaging penalties associated with including both a branch communication valve and one or more wastegate valves in the turbocharger and engine system. Further, there may also be an additional burden on an engine control and monitoring system when two or more valves are implemented and adjusted by the aforementioned system based on engine operating conditions.
The inventors herein have identified an approach to at least partly address the above issue. In one example approach, a method may be provided, comprising adjusting a valve positioned in a passage connecting a first scroll and a second scroll of a turbine to increase an amount of exhaust flow to the turbine when a turbine speed is less than a threshold and during a first load condition, and adjusting the valve to decrease the amount of exhaust flow to the turbine when turbine speed is greater than the threshold, and during a second load condition. In this example, the valve is in fluid communication with a wastegate passage flowing exhaust around the turbine. In this way, an amount of fluidic communication and conveyance between the first scroll and the second scroll, and to the wastegate passage, may be adjusted to provide desired boost pressure based on various engine operating conditions.
For example, the first load condition may include one or more of boost pressure being less than a desired boost pressure, engine load being greater than a threshold load, and torque demand increasing. On the other hand, in another example, the second load condition may include one or more of boost pressure being greater than a desired boost pressure, engine load being less than a threshold load, and torque demand decreasing. By adjusting the single valve, such as a combined branch communication and wastegate valve, to control boost pressure responsive to various engine operating conditions, backpressure and pumping work may also be reduced. Further, additional burden on an engine control and monitoring system may be reduced when the single valve is implemented and adjusted as compared to implementing separate branch communication and wastegate valves.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.